1. Field of the Invention
The present invention relates to computer controlled machine tools and, more particularly, to a system for performing preventative maintenance on such machine tools and for diagnosing abnormal conditions.
2. The Prior Art
In recent years computer controlled machine tools have become more and more common, a large family of such machine tools being referred to generally as numerical controlled or NC machines. Typically these machines are provided with an individual computer which develops control signals for causing the various machine functions to be performed in a prescribed manner at the proper times and for processing feedback signals derived from the machine tool in developing the control signals. Such control signals are used for controlling the various drives for the several axes of the machine tool, typically including servo loops for controlling operation of the machine tool in accordance with a desired program or series of commands.
In some systems, such as the one described and claimed in U.S. Pat. No. 3,777,128 issued to Edward E. Kirkham for "Input Data Sampling Scheme For Computer Controlled Machine Tools," the collection of feedback signals from the machine tool is accomplished only at spaced times, with the control signals being developed during the intervals between such times, thereby freeing the computer much of the time to perform background programs and to execute other operations.
These machines have operated quite successfully, but because of their increased complexity, their maintenance and the diagnosis of abnormal operating conditions, when they occur, is much more difficult than with simpler machine tools. Frequently, precise identification of a faulty component, for the benefit of maintenance and service personnel, is extremely difficult and requires a great deal of time by highly skilled personnel. Successful diagnosis of many abnormal conditions is costly, not only because it is time consuming and requires the services of highly paid personnel, but also because the machine tool being diagnosed is out of service during diagnosis and maintenance. Development of automatic diagnosing and maintenance procedures is not practicable for a user of only a few machines, because of the cost of development and of the additional equipment needed, and the continuing need for highly trained personnel to operate such equipment.
An abnormal condition may take the form of a progressive deterioration in one or another aspect of machine performance, and it sometimes occurs that such deterioration goes unnoticed until it manifests itself in the failure of a fully machined part to meet specifications. It is, therefore, desirable to provide a system by which the foregoing disadvantages may be avoided.